The present invention relates to implant devices and more particularly to percutaneous implant devices.
Early percutaneous devices consisted of a pipe inserted through a surgically created opening in the skin. A sufficiently bio-compatible pipe material permitted such devices to remain in situ for a few weeks to a few months, as long as the devices were not mechanically loaded. However, the weight of conduits and wires passing through these pipes mechanically loaded the pipes. Mechanical loading also resulted from the movement of the patient and handling of the conduit and wires. Such mechanical loading caused stresses and strains along the interface between the percutaneous device and the body tissue. These stresses and strains irritated the tissue and caused local inflammation and tissue destruction. In time, severe epithelial down growth occurred, and the percutaneous device failed.
Early attempts to overcome this difficulty involved the use of particular coatings along the surface of the pipe. These attempts prolonged the useful life of the percutaneous device, but not to the degree necessary for patients needing dialysis or intravenous feeding for many years.
A later attempt to overcome this difficulty focused on the design of different flanges surrounding the pipe. The basic idea of these later attempts was to distribute the forces over a larger area of contact between the skin and the subcutaneous tissue on the one hand and the implant device on the other. Several such flange designs are mentioned and discussed in Grosse-Siestrup et al, "Design Criteria for Percutaneous Devices,"Journal of Biomedical Materials Research, Volume 18, pp. 357-82 (1984). The basic thickness of the flanges shown in FIGS. 18-22, 24 and 25 is uniform, and the flanges are formed of a homogeneous material such as velour loops, woven or knitted structures, etc. (FIG. 22).
Another type of flange mentioned in Gross-Siestrup et al is shown in FIG. 26 and involves a polymer textile fabric, which is uniform in thickness and density. This textile fabric flange is not as stiff as the flanges discussed above and has a stiffness closer to that of the surrounding skin and subcutaneous tissue. However, the stiffness of these textile fabric flanges increases after tissue ingrowth and produces a stiffness discontinuity along the outside rim of these textile fabric flanges. Irritations of the tissue at the flange rim occurs and finally leads to failure of these subcutaneous implants.
U.S. Pat. No. 4,634,422 to Kantrowitz et al discloses a percutaneous access device (FIGS. 6 and 7) with a flange having a peripheral section of reduced uniform thickness, and flanges having a thickness which gradually decreases as one moves radially outwardly from the conduit to the free edge are also known.